1. Field of the Invention
The present invention relates to an exposure mask processing method employing a charged particle beam, and particularly relates to an EPL mask processing method (correction method) using electron beam exposure (ELP; Electron beam Projection Lithography).
2. Description of Related Art
Conventionally, mask patterns are used in patterning processes in semiconductor manufacture of the related art. A mask pattern is usually formed of metal provided on a transparent substrate. Light of wavelengths from visible light to ultra-violet is then used to transfer to the photoresist of the mask pattern. This is then used to carry out patterning of a photoresist applied to a wafer.
However, in recent years, fine-detailing of circuit patterns has advanced and patterning to a higher degree of resolution has therefore been necessary in order to form nano-order circuit patterns. Exposure devices employing electron beams (EB) instead of light have therefore been adopted to meet these demands.
Stencil reticule masks (stencil reticules) where a required exposure window is pierced in a thin film of, for example, silicon or diamond, or silicon carbide, or SiC, etc., are well-known as electron beam exposure masks for when electron beams are employed. These electron beam exposure (EPL: Electron beam Projection Lithography) stencil reticule masks transfer patterns to resists using, for example, 100 kVEB exposure devices.
When stripe-shaped windows, i.e. microscopic holes pre-formed on the stencil reticule mask are not formed according to design, correction of defective windows is carried out because it is necessary to correct window shapes to that of the design. An example employing a charged particle beam processing device in correction of window shapes is disclosed in the document: SPIE 25th Microlithography 2000 (3997-64). According to the device and method disclosed in this document, when the window dimensions opened in this manner are large, this is corrected by deposition, while on the other hand, when the dimensions of the opened window are small, this can be corrected by etching. The mask pattern dimensions are in the order of approximately 100 nm line and space, and processing precision in the order of 10 nm is required. Further, the mask thickness is usually in the order of 0.5 to 2 μm, with high-aspect ratio processing being required for this correction. To achieve this, during processing (etching or deposition) for correcting the stencil reticule masks, particles such as etching shavings or deposition matter etc. become attached onto side-wall surfaces other than the side wall surfaces being processed. A window having a clean wall surface therefore cannot be obtained.
This adhesion has accompanied the densification of LSIs in recent years and the influence of this adhesion cannot now be ignored. It is therefore necessary to remove the attached matter (or attached particles).
A simple description is now given of a related example for carrying out correction processing on a stencil reticule mask (hereinafter referred to simply as “mask”) for removing the attached matter. Well known conventional examples of charged particle beam irradiation devices used in the related art are devices including display devices, for example, including SEMs (scanning electron microscopes) for automatically deciding the positioning of a mask to be processed and an irradiating charged particle beam, and control devices for designating a region displayed on a monitor screen to be subjected to correction processing and automatically controlling a charged particle beam to irradiate within this designated region.
These kinds of display devices and control devices are well known and their detailed description is therefore omitted.
FIG. 1 shows a typical process for a process where this attachment occurs and an elimination step thereof. A detailed description is now given with reference to FIG. 1 of the occurrence of attached matter and its removal in the related art.
FIG. 1(A) is a partial plan view showing a mask having a window to be corrected. A window 40 is formed in the mask 10 but a projection 42 remains on part of a sidewall 40b of two facing sidewalls 40a and 40b of this window 40, rendering the window defective. The projection 42 is eliminated through etching, and it is desired to correct the window shape to the designed window shape. In the drawing, an opening 12 is shown between the tip of the projection 42 and the other sidewall 40a. 
FIG. 1(B) to FIG. 1(E) are enlarged outline views showing the state of a stencil reticule mask when setting a processing frame. FIG. 1(B) to FIG. 1(E) are views showing a cross-section of a stencil reticule mask 10 within a plane including a central axis of the extracted charged particle beam, taken along line I—I of FIG. 1(A).
<FIG. 1(B): Setting the Processing Frame>
The projection 42 to be removed by etching is designated. This designation is principally carried out in order to indicate that the final line for where the projection 42 is removed by etching is one sidewall 40b of the window 40 as designed. This etching processing is usually carried out while viewing a typical monitor display screen, with the processing frame (eliminated region) set on the display screen shown by a dashed line 20 overlaid on the drawing. The tip of the projection 42 is shown in the drawing as 12a. 
<FIG. 1(C): During Processing>
Irradiation of the extracted charged particle beam 30 takes place sequentially from above in the X-direction in the drawings at the region of the projection 42 of the mask 10 on the side within the processing frame 20 from the side of the end surface thereof. When an etching surface (referred to as a “correction processed surface”) 12b is formed accompanying etching of the projection 42 by irradiation, shavings 14, i.e. eliminated matter, flies off in all directions (spherically). This eliminated matter 14 becomes affixed to the other sidewall 40a facing the window 40 and is deposited so as to form a deposited layer 14a (refer to FIG. 1(C)).
<FIG. 1(D): When Processing Finishes>
Etching processing using the charged particle beam as described above is carried out in order in the X-direction as shown in FIG. 1(C). This etching surface is one wall surface (sidewall) 40b of the window 40. As a result of the completion of this correction processing, a correction complete window 40 for electron exposure, is formed having a gap width as designed between the facing sidewalls 40a and 40b. During the processing in the correction processing described above in FIG. 1(B) to FIG. 1(D), flying particles of eliminated matter 14 are deposited on the sidewall 40a, and a deposited layer 16 is formed of eliminated matter (shavings) 14 on the sidewall 40a of the window 40.
<FIG. 1(E): Elimination of the Deposited Layer>
Conventionally, this deposited layer 16 is collectively eliminated using the charged particle beam 30 after finishing correction processing of the window 40. Accompanying this removal, newly created eliminated matter 18 is deposited on the etching surface of sidewall 40b and a re-attached layer 18a is formed. This re-attached layer 18a is then removed using the charged particle beam 30.
In this manner, elimination of successively attached matter is complete.
However, in the related method described above, elimination of re-attached matter is carried out immediately after completion of the correction processing. There is therefore the problem that when a certain amount of re-attached matter is deposited, then elimination of the re-attached matter becomes time consuming.
In addition, in the step for eliminating re-attached matter, there is the fear that new attached matter (re-attached matter) may appear in this vicinity.
In order to resolve the aforementioned problems, the present invention sets out to provide an EPL mask processing method for processing a mask pattern in such a manner that re-attached matter occurring when a charged particle beam processing device is employed in mask processing used in an electron beam exposer device is eliminated in a precise and efficient manner.